Male rats were exposed to 2.45 GHz microwave, radiation at an incident power density of 10 mW/cm squared (SAR = 2 mW/g) daily for 3 hours from day 4 of pregnancy (in utero) through day 40 post partum. The animals were killed and the brains were removed, weighed, measured and histologically examined at 15, 20, 30 and 40 days of age. The results showed that there was no significant effect on brain development due to exposure during the embryonic, fetal and postnatal period. Japanese quail eggs were continuously exposed to 2.45 GHz microwave radiation from day 1 through day 12 of incubation (5 mW/cm squared SAR = 4.03 mW/g). Irradiated and control embryos were removed on day 12, 13 or 14 of incubation, and the cerebella were histologically examined. In order to determine the effects of microwave exposure during embryogenesis on subsequent development of the cerebellum, some of the quail were allowed to hatch and reared to 8 weeks of age. Irradiated embryos exhibited a slight development retardation in the cerebellar cortices in terms of several morphological parameters. In the 8 week old quail, no significant differences were noted between irradiated and control cerebella in the morphological measurements of Purkinje cells.